Nicola J. Flack

Uterine artery blood flow response to correction of amniotic fluid volume

OBJECTIVE Our purpose was to investigate whether acute alterations of amniotic fluid volume affect uteroplacental perfusion. STUDY DESIGN Three groups of patients of comparable gestational age were studied in a fetal medicine referral unit: (1) eight pregnancies with severe polyhydramnios because of twin-twin transfusion syndrome undergoing therapeutic amnioreduction, (2) seven with severe oligohydramnios undergoing diagnostic amnioinfusion, and (3) six control women having invasive procedures of similar duration without manipulation of amniotic fluid volume. Color Doppler imaging was used to measure uterine artery impedance index values and quantitative blood flow before and within 15 minutes of the end of the procedure. RESULTS Quantitative flow measurements increased after amnioreduction (74% median increase of volume flow, range 22% to 329%, p < 0.01) and decreased after amnioinfusion (33% median decrease of volume flow, range 17% to 51%, p < 0.05). Impedance index values increased after amnioinfusion (25% median increase in pulsatility index, range 4% to 71%, p < 0.05) and did not alter with amnioreduction. There were no significant changes in the control group. CONCLUSION Acute changes in amniotic fluid volume alter uteroplacental perfusion. In twin-twin transfusion syndrome amelioration in uterine flow may improve fetal condition and explain in part the success of serial amnioreduction therapy.

Acute maternal hydration in third-trimester oligohydramnios: Effects on amniotic fluid volume, uteroplacental perfusion, and fetal blood flow and urine output

OBJECTIVE Our purpose was to determine whether acute maternal hydration in pregnancies with third-trimester oligohydramnios (1) increases amniotic fluid index and hourly fetal urine production rate and (2) alters uteroplacental perfusion and fetal blood flow. STUDY DESIGN Ten women with third-trimester oligohydramnios (amniotic fluid index < or = 5 cm) and 10 controls with normal amniotic fluid volume (amniotic fluid index > 7 cm) were prospectively recruited for this study. Maternal plasma and urine osmolality, amniotic fluid index, hourly fetal urine production rate, and Doppler flow velocimetry of maternal uterine artery and fetal umbilical, descending aorta, middle cerebral, and renal arteries were determined before and after oral hydration by having the patient drink 2 L of water over 2 hours. RESULTS There was a significant reduction in maternal plasma (p < 0.05) and urine osmolality (p < 0.0001) in both groups after short-term oral hydration. Hydration increased amniotic fluid volume in women with oligohydramnios (mean change in amniotic fluid index 3.2 cm, 95% confidence intervals 1.1 to 5.3; p < 0.02) but not in those with normal amniotic fluid volume (mean change in amniotic fluid index -2.0, 95% confidence intervals -4.1 to +0.2). The hourly fetal urine production rate, however, did not increase in either group (mean change in hourly fetal urine production rate 3.5 ml/hr, 95% confidence intervals -11.7 to +18.7 and -6.8 ml/hr, 95% confidence intervals -2.9 to -10.7, respectively). Hydration was associated with an increase in uterine artery mean velocity in the oligohydramnios group (mean change in mean velocity 16.7 cm/sec, 95% confidence intervals 8.0 to 25.3; p < 0.006) but not in controls (mean change in mean velocity 1.2 cm/sec, 95% confidence intervals -19.7 to +22.1). There was no change in pulsatility index or in velocity in any of the fetal vessels studied in either group. CONCLUSIONS Short-term maternal oral hydration increases the amniotic fluid index in women with third-trimester oligohydramnios. Although the mechanism for this effect remains unclear, it could not be accounted for by fetal urination in this study but instead was associated with improved uteroplacental perfusion.

Accuracy of prenatal diagnosis of renal agenesis with color flow imaging in severe second-trimester oligohydramnios

OBJECTIVE Our purpose was to examine the potential of color flow imaging to assess the presence of renal arteries in second-trimester pregnancies complicated by severe oligohydramnios. STUDY DESIGN Thirty-three consecutive second-trimester pregnancies referred with severe oligohydramnios were prospectively studied with high-resolution color Doppler ultrasonography to establish the presence or absence of renal arteries. Prenatal findings were correlated with the presence or absence of fetal kidneys at postmortem or postnatal examination. RESULTS Neither renal artery was visualized in eight fetuses; postmortem examination confirmed bilateral renal agenesis in seven and unilateral renal agenesis with a contralateral atrophic multicystic kidney in the other. Only one renal artery was seen in three; postmortem examination demonstrated unilateral renal agenesis in two fetuses and bilateral multicystic dysplastic kidneys in the other. Postmortem or postnatal evaluation confirmed the presence of both kidneys in all 22 fetuses in which both renal arteries were identified prenatally. CONCLUSIONS Color Doppler ultrasonography is useful in the prenatal evaluation of fetuses with severe second-trimester oligohydramnios to demonstrate the presence or absence of renal arteries. This technique should be added to the armamentarium of prenatal tests to evaluate second-trimester fetuses with severe oligohydramnios.

Amiodarone given by three routes to terminate fetal atrial flutter associated with severe hydrops

Background: We describe the concurrent administration of amiodarone using three different routes in order to provide: 1) rapid and adequate fetal loading without giving unduly high doses to the mother, and 2) a maintenance dose to the fetus without risking repeated invasive procedures.

The influence of operator transducer pressure on ultrasonographic measurements of amniotic fluid volume

OBJECTIVE Our purpose was to study the effect of operator transducer pressure on amniotic fluid index and single deepest pool measurements and their intraobserver and interobserver variability. STUDY DESIGN Forty subjects in the third trimester with intact membranes were studied by two observers at three predetermined operator pressures. Pressure was measured by interfacing a flexible water-filled reservoir connected to a manometer between the maternal abdomen and the ultrasonography transducer. The amniotic fluid index and single deepest pool were measured on screen by another operator, and data were analyzed by calculating components of variance. RESULTS Compared with medium pressure, low pressure resulted in a 13% increase in amniotic fluid index (p < 0.001), and high pressure resulted in a 21% fall in amniotic fluid index (p < 0.001). The single deepest pool was less sensitive to pressure, with a 11% increase at low pressure (p < 0.001) and a 16% fall at high pressure (p < 0.001). Intraobserver error was 17% for amniotic fluid index and 18% for single deepest pool when operator pressure was controlled at medium pressure; this increased to 28% and 24%, respectively, when pressure was not controlled (p < 0.01). Interobserver error was consistently very low. CONCLUSION Both techniques are highly sensitive to the pressure applied to the maternal abdomen during scanning. The reproducibility of amniotic fluid index and single deepest pool is comparable. The use of the same observer for serial measurements of amniotic fluid index would appear to be less important than careful attention to transducer pressure.

Direct volume measurement at midtrimester amnioinfusion in relation to ultrasonographic indexes of amniotic fluid volume.

OBJECTIVE Our purpose was to investigate the relationship between amniotic fluid volume and semiquantitative ultrasonographic assessment of amniotic fluid in the midtrimester. STUDY DESIGN Sixteen pregnancies between 16 and 28 weeks with minimal amniotic fluid (severe oligohydramnios or anhydramnios) and intact membranes were studied at the time of clinically indicated amnioinfusion. The amniotic fluid index and deepest pool measurement were determined before and immediately after the procedure. Correlations were sought by means of standard regression techniques with amniotic fluid volume (i.e., volume infused) on the basis of the assumption that amniotic fluid volume before amnioinfusion was effectively nil. RESULTS There was a significant linear relationship between amniotic fluid index and volume infused (y = 7.336 + 0.015x; R2 = 0.30, p < 0.05). However, no correlation with the deepest pool measurement technique was found (R2 = 0.11, p > 0.05). CONCLUSION Amniotic fluid index is preferable to deepest pool measurement in assessing amniotic fluid volume in the second trimester of pregnancy. The low variance (30%) suggests that better predictors of amniotic fluid volume are still required.

Discordant iliac and femoral artery flow velocity waveforms in fetuses with single umbilical artery

OBJECTIVE The aim of this study was to investigate pelvic and femoral arterial flow velocity waveforms in fetuses with a single umbilical artery. STUDY DESIGN Seven fetuses with single umbilical artery and no other ultrasonographically detected anomalies were studied with color Doppler ultrasonography at a median gestational age of 24 weeks (range 18 to 34 weeks). Flow velocity waveforms from the relevant vessels were obtained as follows: (1) umbilical artery from a free loop of cord, (2) common iliac artery from both sides just below the aortic bifurcation, (3) internal iliac artery and intraabdominal portion of the umbilical artery from the vessel visualized alongside the fetal bladder, and (4) femoral artery on both sides from the upper third of the fetal thigh. The pulsatility index was measured, and comparisons were made with the paired t test. A p value < 0.05 was considered significant. RESULTS The pulsatility index in the umbilical artery was normal in all cases. There were highly significant differences between the common iliac arteries in each side (difference in pulsatility index 2.7, 95% confidence interval 2.0 to 3.5, p < 0.001). Significant differences between both femoral arteries were also noted (difference in pulsatility index 1.0, 95% confidence interval 0.3 to 1.7, p < 0.001). In both vessels the pulsatility index was always higher in the side that did not participate in the placental circuit. CONCLUSION This study demonstrates that fetuses with single umbilical artery have asymmetric arterial blood flow patterns in the pelvic and lower extremities.

Oligohydramnios and associated fetal complications

During intrauterine life the fetus is bathed in amniotic fluid which provides a low resistance space for free movement and a buffer against external trauma. This fluid is produced in early pregnancy largely as a maternal dialysate, then as a fetal transudate. Fetal urine is the most important source of amniotic fluid after 16 weeks gestation. The control of amniotic fluid is complex and poorly understood; it arises from secondary partitioning of water within the fetoplacental extracellular space and reflects fetal fluid balance.